This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-370603, filed Dec. 27, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a semiconductor integrated circuit, and, more particularly, to a semiconductor integrated circuit with an amplifier circuit which has a wide dynamic range even for a low voltage source.
As the microminiaturization of the semiconductor process progresses, the state-of-the-art LSI circuit technology is demanded of a faster operational speed of integrated circuits, lower power consumption and lower supply voltages. While the improvement on the operational speed and the reduction in power consumption have been accomplished by the device technology, the circuit performance in lower supply voltages cannot be guaranteed by the device technology and should be achieved by the circuit technology.
In analog circuits, particularly, as the supply voltages become lower, it becomes difficult to improve the signal dynamic range and secure the good S/N (signal to noise) ratio. For example, a conventional amplifier circuit in a semiconductor integrated circuit shown in FIG. 1A comprises a basic OTA (Operational Transconductance Amplifier) 1 and a load resistor 2 as shown in FIG. 2. Given that the mutual conductance of the OTA 1 is gm, the amplifier circuit outputs current i (=gmxc2x7Vin) proportional to an input voltage Vin. The current i is supplied to the load resistor 2 and Vin is amplified by gmxc2x7rL, yielding an amplified output voltage Vout.
The amplitude of the output voltage Vout that appears at an output terminal 101 is generally limited to (Vmaxxe2x88x92Vmin) by voltage values Vmax and Vmin according to supply voltages (VDD, xe2x88x92VSS) as shown in FIG. 1B. Therefore, the reduction in supply voltages reduces the dynamic range of an analog signal Vout, thus making it difficult to secure the performance of the amplifier circuit.
Conventionally, various attempts have been made to reduce the supply voltages. The attempts include the generation of a high voltage by a booster circuit (DC-DC converter, boost trap circuit or the like), and designing a folded type circuit or a low-voltage circuit which uses MOS transistors having a low threshold value. The booster circuit raises a problem of a breakdown voltage in the microminiaturization or sub-micron process. The folded type circuit generally suffers a complicated circuit design. MOS transistors with a low threshold value often produce a leak current which should be coped with. Those techniques often stand in the way of designing an analog circuit into an integrated circuit in the microminiaturization process, and do not always provide a solution to securing the dynamic range in analog signal processing.
Apparently, as the supply voltages become lower, it becomes difficult to improve the signal dynamic range and secure the good S/N ratio in accordance with the reduction in supply voltages. In an amplifier circuit, particularly, the reduction in supply voltages reduces the dynamic range of an analog signal. This makes it difficult to secure the performance of the amplifier circuit.
It is an object of the present invention to provide a semiconductor integrated circuit that can realize an amplifier circuit having a wide effective dynamic range even for low supply voltages and that can realize an amplifier circuit having a wide dynamic range using the ordinary CMOS semiconductor circuit technology.
According to a first aspect of this invention, there is provided a semiconductor integrated circuit for a low supply voltage, which comprises an amplifier circuit including a current output type amplifier converting an input signal to a current signal, a load resistor having one end connected to an output terminal of the current output type amplifier and a voltage control circuit having an input terminal connected to the one end of the load resistor and an output terminal connected to the other end of the load resistor, an input terminal of the amplifier circuit serving as an input terminal of the current output type amplifier, output terminals of the amplifier circuit serving as the individual ends of the load resistor.
The following are preferable embodiments of the first aspect of the invention.
(1) The voltage control circuit comprises a first functional circuit which fixes an output voltage to a preset first constant voltage when an input voltage is higher than the first constant voltage and operates as an inverting operational amplifier when the input voltage is lower than the first constant voltage.
(2) The voltage control circuit comprises a second functional circuit which fixes an output voltage to a preset second constant voltage when an input voltage is lower than the second constant voltage and operates as an inverting operational amplifier when the input voltage is higher than the second constant voltage.
(3) The voltage control circuit comprises a third functional circuit which operates as an inverting operational amplifier.
According to a second aspect of this invention, there is provided a semiconductor integrated circuit for a low supply voltage, which comprises an amplifier circuit including a current output type amplifier converting an input signal to a current signal, a first resistor having one end connected to an output terminal of the current output type amplifier, a first voltage control circuit having an input terminal connected to the one end of the first resistor, a second resistor having one end connected to the output terminal of the current output type amplifier, and a second voltage control circuit having an input terminal connected to the one end of the second resistor and an output terminal connected to the other end of the second resistor. The amplifier circuit has an input terminal serving as an input terminal of the current output type amplifier and output terminals serving as the output terminal of the current output type amplifier and the other ends of the first and second resistors.
The second aspect of the present invention may take the form of the following preferable embodiment.
The second voltage control circuit comprises a first functional circuit which fixes an output voltage to a preset first constant voltage when an input voltage is higher than the first constant voltage and operates as an inverting operational amplifier when the input voltage is lower than the first constant voltage, and the first voltage control circuit is constituted by a second functional circuit which fixes the output voltage to a preset second constant voltage higher than the first constant voltage when the input voltage is lower than the second constant voltage and operates as an inverting operational amplifier when the input voltage is higher than the second constant voltage.
According to a third aspect of this invention, there is provided a semiconductor integrated circuit for a low supply voltage, which comprises an amplifier circuit including a current output type amplifier converting an input signal to a current signal, a first resistor having one end connected to an output terminal of the current output type amplifier, a first voltage control circuit having an input terminal connected to the one end of the first resistor, a second resistor having one end connected to the output terminal of the current output type amplifier, and a third voltage control circuit having an input terminal connected to the other end of the first resistor and an output terminal connected to the other end of the second resistor. The amplifier circuit has an input terminal serving as an input terminal of the current output type amplifier and output terminals serving as the output terminal of the current output type amplifier and the other ends of the first and second resistors.
The following are preferable embodiments of the third aspect of the invention.
(1) The first voltage control circuit comprises a first functional circuit which fixes an output voltage to a preset first constant voltage when an input voltage is higher than the first constant voltage and operates as an inverting operational amplifier when the input voltage is lower than the first constant voltage, and the third voltage control circuit is constituted by a fourth functional circuit which fixes the output voltage to the first constant voltage when the input voltage is lower than a preset second constant voltage higher than the first constant voltage and operates as a non-inverting operational amplifier when the input voltage is higher than the second constant voltage.
(2) The first voltage control circuit comprises a second functional circuit which fixes an output voltage to a preset second constant voltage when an input voltage is lower than the second constant voltage and operates as an inverting operational amplifier when the input voltage is higher than the second constant voltage. The third voltage control circuit is constituted by a fifth functional circuit which fixes the output voltage to the second constant voltage when the input voltage is higher than a preset first constant voltage lower than the second constant voltage and operates as a non-inverting operational amplifier when the input voltage is lower than the first constant voltage.
According to a fourth aspect of this invention, there is provided a semiconductor integrated circuit for a low supply voltage, which comprises an amplifier circuit including a current output type amplifier converting an input signal to a current signal, a first resistor connected to an output terminal of the current output type amplifier, a differential operational amplifier having a positive input terminal applied with a constant voltage, a negative input terminal connected to one end of the first resistor and an output terminal connected to the other end of the first resistor, a second resistor having one end connected to the output terminal of the current output type amplifier, and a third voltage control circuit having an input terminal connected to the other end of the first resistor and an output terminal connected to the other end of the second resistor, and wherein the input terminal of the amplifier circuit serves as an input terminal of the current output type amplifier, and the output terminals of the amplifier circuit serve as the output terminal of the current output type amplifier and the other ends of the first and second resistors.
The following are preferable embodiments of the fourth aspect of the invention.
(1) The third voltage control circuit comprises a fourth functional circuit which fixes an output voltage to a preset first constant voltage when an input voltage is lower than a preset second constant voltage higher than the first constant voltage and operates as a non-inverting operational amplifier when the input voltage is higher than the second constant voltage.
(2) The third voltage control circuit comprises a fifth functional circuit which fixes an output voltage to a preset second constant voltage when an input voltage is higher than a preset first constant voltage lower than the second constant voltage and operates as a non-inverting operational amplifier when the input voltage is lower than the first constant voltage.
(3) The semiconductor integrated circuit further comprises a third resistor having one end connected to the output terminal of the current output type amplifier and a fourth voltage control circuit having an input terminal connected to the other end of the second resistor and an output terminal connected to the other end of the third resistor. The output terminal of the current output type amplifier, the other ends of the first and second resistors and the other end of the third resistor serve as an output terminal of the amplifier circuit.
(4) The third and fourth voltage control circuits comprise a fourth functional circuit which fixes an output voltage to a preset first constant voltage when an input voltage is lower than a preset second constant voltage higher than the first constant voltage and operates as a non-inverting operational amplifier when the input voltage is higher than the second constant voltage.
(5) The third and fourth voltage control circuits comprise a fifth functional circuit which fixes an output voltage to a preset second constant voltage when an input voltage is higher than a preset first constant voltage lower than the second constant voltage and operates as a non-inverting operational amplifier when the input voltage is lower than the first constant voltage.
(6) The differential operational amplifier is replaced with a third functional circuit which operates as an inverting operational amplifier.
With the above-described structures, the present invention may take the forms of the following preferable embodiments.
(1) The first functional circuit comprises an operational amplifier constituted by a differential stage for applying an input voltage to one of a pair of differential inputs formed by a pair of MOS transistors of a first channel, supplying the first constant voltage to the other differential input and having a pair of MOS transistors of a second channel opposite to the first channel as a load; an output stage including a source follower comprised of an MOS transistor of the first channel and a load; and a circuit connected to an output terminal of the output stage, for fixing a voltage at the output terminal of the output stage to the first constant voltage when that voltage is lower than the first constant voltage. The inverted signal of the input voltage to the operational amplifier is output to the output terminal of the output stage.
(2) The second functional circuit comprises an operational amplifier constituted by a differential stage for applying an input voltage to one of a pair of differential inputs formed of a pair of MOS transistors of a first channel, supplying the second constant voltage to the other differential input and having a pair of MOS transistors of a second channel opposite to the first channel as a load; an output stage including a source follower comprised of an MOS transistor of the second channel and a load; and a circuit connected to an output terminal of the output stage, for fixing a voltage at the output terminal of the output stage to the second constant voltage when that voltage is higher than the second constant voltage. The inverted signal of the input voltage to the operational amplifier is output to the output terminal of the output stage.
(3) The third functional circuit comprises an inverting operational amplifier constituted by connecting an input resistor and a feedback resistor to an operational amplifier and a voltage follower connected to an input terminal of the inverting operational amplifier. The input terminal of the third functional circuit serves as an input terminal of the voltage follower and the output terminal of the third functional circuit serves as an output terminal of the inverting operational amplifier.
(4) The third functional circuit comprises an inverter comprising MOS transistors.
(5) The fourth functional circuit comprises an operational amplifier constituted by a differential stage for applying an input voltage to one of a pair of differential inputs formed of a pair of MOS transistors of a first channel, supplying the second constant voltage to the other differential input and having a pair of MOS transistors of a second channel opposite to the first channel as a load; an output stage including a source follower comprised of an MOS transistor of the first channel and a load; and a circuit connected to an output terminal of the output stage, for fixing a voltage at the output terminal of the output stage to the first constant voltage when that voltage is lower than the first constant voltage. The non-inverted signal of the input voltage to the operational amplifier is output to the output terminal of the output stage.
(6) The fifth functional circuit comprises an operational amplifier constituted by a differential stage for applying an input voltage to one of a pair of differential inputs formed of a pair of MOS transistors of a first channel, and supplying the first constant voltage to the other differential input and having a pair of MOS transistors of a second channel opposite to the first channel as a load; an output stage fabricated by a source follower comprised of an MOS transistor of the second channel and a load; and a circuit connected to an output terminal of the output stage, for fixing a voltage at the output terminal of the output stage to the second constant voltage when that voltage is higher than the second constant voltage. The non-inverted signal of the input voltage to the operational amplifier is output to the output terminal of the output stage.
(7) The individual output terminals of the amplifier circuit are connected to an A/D converter formed on the same semiconductor integrated circuit.
According to this invention, a voltage control circuit which converts and controls the voltages at the input and output terminals as needed in accordance with an input signal is provided in an amplifier circuit, so that the input/output voltage of the voltage control circuit falls within a predetermined voltage range. This makes it possible to disperse the output signal to two (or three or more) voltage ranges in a predetermined low voltage range in signal conversion. Therefore, a circuit operable on low supply voltages can amplify a signal with a wide dynamic range. Further, the output signal that is not limited to the supply voltages is obtainable. This can ensure analog signal processing with a wide effective dynamic range.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.